www.4x4mart.co.uk
FEBRUARY 2011 | 4x4 MART
73
TECHNICAL: 4x4 TYRES
TECH TALK
GETTING TO GRIPS How capable your vehicle is when driving off-road or in wintry conditions can be hugely affected by your choice of tyres. Paul Guinness offers some nononsense advice
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nybody who goes off-roading on a regular basis will already know how important the right choice of tyre is for their vehicle’s progress (or otherwise) in the rough. And as Britain has been enduring yet another harsh winter, attention has also turned to the subject of snow tyres – and how choosing the right tyres can mean the difference between getting around and being stranded. In choosing a tyre, there’s obviously more to consider than the terrain over which you may be driving. The Road Vehicles (Construction & Use) Regulations 1986, for example, have clauses relating to the types of tyres that can legally be fitted to a vehicle. There are restrictions on which vehicles can be fitted with retread or remould tyres, and there are obviously statutory levels of tread necessary for legal road use – which usually means 1.6mm throughout a continuous band comprising the central three
quarters of the tread, round the entire circumference of the tyre. When it comes to tyre upgrades for your 4x4, however, there’s usually one major requirement: to increase your vehicle’s capabilities over rough terrain. Yes, for most of us it’s all about grip, which means the focus is very much on your tyre tread – with AllTerrain tyres being the default choice for many 4x4 owners who need good on-road performance and comfort coupled with off-road competence. And although All-Terrain tyres (generally specified for 50 per cent onand 50 per cent off-road use) don’t look particularly ‘extreme’, their abilities are usually very impressive. For serious off-road use on a regular basis (perhaps an 80/20 split in favour of off-roading), you need to be looking at MT (Mud Terrain) or M&S (Mud and Snow) tyres. Large shoulder blocks – the chunks of rubber castellating the tyre’s external diameters – cut into
terrain, afford traction on slippery surfaces and adapt their function to all kinds of conditions. Meanwhile, alternating inward and outward tread blocks within the external and internal shoulder-blocks mean these tyres can exert a cog-like force, ‘pulling’ their own mass over an obstacle as long as impetus is given to the wheel. The depth of an off-road tyre’s tread is also greatly increased, the biggest give-away to its purpose, as this prevents clogging. The disadvantage to ‘knobblies’ like these, however, is in their construction: large, chunky composition means that resistance to pressure gives a very hard ride, and the increase in noise levels is dramatic. Sidewalls, exposed to rocks and rough terrain, are also heftily reinforced, which again affects your 4x4’s ride comfort – although if off-road mobility is your primary aim, you’re unlikely to be worried by any such issues.